End Dragon spawns multiple times, goes to normal, then repeats.

I have been playing in a Minecraft seed for a while now, and I found the end. My problem is I went to the end and multiple end dragons kept spawning in. It stayed like that for a while until I left the game for a few hours to do something. It reverted back to normal when I went back in. Well then 5 (or more) dragons spawned in and I was baffled by it, and am now unable to complete the game. A few other of my friends have also encountered this.